Durability should be the same for a Mtn. Gun and any other Smith .44 Mag., IMO. The frame is the same, the cylinder is fluted, but the strength of the cylinder is determined by the bolt notches, not the flutes. The skinny barrel should not be a factor.
The gun does kick--it's more fierce than any other .44 Mag. I own, including the 3" barrel M29. But (and it's a big but) it's great for carrying hunting--the barrel is 4 inches, BTW. It's especially good in a situation where you're carrying a rifle also (or a camera mounted on a tripod).
Work up a good practice load (light) which shoots to the same POA as the hunting load and it's a great companion. I love the concept.